Method for arranging transmissions on a downlink carrier

ABSTRACT

A method is provided for arranging transmissions on a downlink carrier c, spanning a frequency range Fc, in a mobile radio communications system, wherein a bandwidth of Fc belongs to a set of predefined channel bandwidths in the communications system, and wherein the carrier c comprises a reference signal defined in the communications system. A configurable frequency range FRS comprising a set of time-frequency resources for comprising the reference signal of the carrier c is provided. Information associated with the configuration of said frequency range FRS is signaled to a receiver in the communications system, such that c can be deployed over a frequency range F smaller than Fc when the frequency range FRS is configured within F and any other transmissions on the carrier c are arranged to be within F.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/CN2011/072941, filed on Apr. 18, 2011, which is hereby incorporatedby reference in its entirety.

FIELD OF THE INVENTION

The present invention concerns a method for arranging transmissions on adownlink carrier in a mobile radio communications system. Further, itconcerns a radio base station and a mobile terminal.

BACKGROUND ART

A wireless cellular communication system typically comprises one orseveral radio carriers, on which information is transmitted. Thebandwidth of a radio carrier would have to be chosen such that it can beaccommodated within the spectrum resources the system operator has atits disposal. The spectrum allocated to a certain system operator isoften a consequence of national regulatory decisions and may betechnology neutral.

Unfortunately, the carrier bandwidths that radio communications systemscan provide have always limited flexibility. For example, the 3GPP LongTerm Evolution (LTE) standard (E-UTRA) uses Orthogonal FrequencyDivision Multiplex (OFDM) transmission which in principle allows forvery flexible transmission bandwidth by configuring a suitable number ofOFDM subcarriers. However, for each bandwidth configuration it is neededto specify performance requirements for various channels, spectral masksfor out-of-band emissions, test cases for transmitters and receivers,etc, which increases the cost and complexity of the equipment. Thusmaking a large number of bandwidth configurations specified by astandard is not practical. This is the reason why only six channelbandwidths are currently supported in LTE: 20, 15, 10, 5, 3 and 1.4 MHz.

In a number of real-life LTE deployment cases it has been alreadynoticed that these bandwidths do not perfectly match the spectrumallocations available to the operators. For example, if 19 MHz isavailable, the largest single-carrier LTE bandwidth that can be deployedis 15 MHz. The remaining 4 MHz can either not be used for LTE or can bepartially used by deploying an additional LTE carrier with 3 MHz carrierbandwidth. Multiple carriers can be aggregated for transmission andreception to one user. This co-called carrier aggregation solution isspecified in Rel. 10 of the LTE standard, which however demands specialcategories of mobile terminals. If a terminal is not capable of carrieraggregation, it would have to use either the 3 MHz or the 15 MHzcarrier, which will limit its maximum throughput.

The additional problem for the operators is that not all carrierbandwidths are supported by the LTE standard in all frequency bands, socarrier aggregation will not always be possible. In the given example a3 MHz LTE carrier might not be possible to deploy in the remainingspectrum because all the carrier bandwidths are not defined in allfrequency bands. Even if carrier aggregation is used as in the aboveexample, there could still be left-over spectrum that is not used, sothis obviously is not the most efficient solution. Thereto, with carrieraggregation, parts of the spectrum have to be used as guard band betweencarriers.

Introducing new transmission bandwidth configurations could provide away to use the available bandwidth more efficiently. However, set asidethe issues with standardization and testing, it would also be a problemto determine suitable values for new bandwidth configurations that wouldfit most system deployments world wide. It should also be noted that newbandwidth configurations will not be accessible to terminals presentlyin use, but only to terminals of releases of the system, for which thenew bandwidth configuration has been introduced. Hence, introducing newtransmission bandwidth configurations poses problems for systemoperators that already have deployed a system, as different carrierswill be accessible to terminals of different system releases.

Two types of solutions for improving the spectrum utilization have beenproposed in the past for the prior art LTE system: carrier segments andextension carriers.

The carrier segments are contiguous bandwidth extensions to a normal LTEcarrier. This solution implies that the normal LTE carrier bandwidth issmaller than the available amount of spectrum, so that the segments canbe deployed in the remaining parts. The segments can be used either foruser data transmission or for the transmission of some new controlchannels that might be defined in the future releases of the standard.The sum of the channel bandwidths of the normal LTE carrier and thesegments cannot be larger than 20 MHz, because one control channel(located on the normal LTE carrier) is used for scheduling transmissionon both the normal LTE carrier and the segments, while the controlchannel of the normal LTE carrier cannot handle resource allocation forlarger channel bandwidths. Since only one control channel is used, onlyone Hybrid Automatic Repeat reQuest (HARQ) process is utilized, and thesame transmission mode is used on the segment as on the normal LTEcarrier. It has been proposed that the size of the segments is limitedto be the same as the channel bandwidths supported in LTE; 20, 15, 10,5, 3 and 1.4 MHz.

The extension carrier is defined as a supplementary component carrier tothe normal LTE carrier, which serves only for user data traffictransmission. The corresponding control information is transmitted overthe control channels allocated on a normal LTE carrier. It was alsosuggested that an extension carrier or a carrier segment does notinclude broadcast channels, synchronization signals and the commonreference signals (CRS). It means that extension carrier cannot beoperated stand-alone and must be part of carrier aggregation. As opposedto carrier segments, there is no restriction on the sum of normal LTEcarrier bandwidth and extension carrier bandwidth, except that each ofthem can be at most 20 MHz. Furthermore, an extension carrier does notneed to be located contiguously to the normal LTE carrier. The extensioncarrier is scheduled from the normal LTE carrier but using a separatecontrol channel, i.e., there is a separate control channel forscheduling transmissions on an extension carrier and another one forscheduling transmissions on a normal LTE carrier. Since the extensioncarrier has a separate control channel, it also has a separate HARQprocess, and different transmission modes can be used on the extensioncarrier and the normal LTE carrier. It has been proposed that theextension carrier bandwidth can be configured the same as the channelbandwidths supported in LTE; 20, 15, 10, 5, 3 and 1.4 MHz.

However, when the bandwidth of an available spectrum resource does notmatch a combination of supported bandwidths, there is still a waste ofsuch spectrum resources that will be left unused. For instance, in thecase of LTE, a spectrum resource of 19 MHz configured with a componentcarrier of 15 MHz and a carrier segment or extension carrier of 3 MHzstill leaves 1 MHz unused.

SUMMARY OF THE INVENTION

It is an object of the present invention to propose a solution for or areduction of the problems of prior art. A main object is consequently toprovide for a better usage of available spectrum resources for radiocommunications systems.

According to the invention this is accomplished with a method forarranging transmissions on a downlink carrier c, spanning a frequencyrange F_(c), in a mobile radio communications system, wherein abandwidth of F_(c) belongs to a set of predefined channel bandwidths inthe communications system, and wherein the carrier c comprises a set ofreference signals defined in the communications system. The method isdistinguished by:

-   -   providing a configurable frequency range F_(RS) comprising a set        of time-frequency resources for comprising the reference signals        of the carrier c, and    -   signaling information associated with the configuration of said        frequency range F_(RS) to a receiver in the communications        system.

The method enables that the carrier c can be deployed over a frequencyrange F that is smaller than F_(c) when:

-   -   the frequency range F_(RS) is configured within F and    -   any other transmissions on the carrier c are arranged to be        within F.

Thus, it is realized that to maximize the spectrum utilization anddeployment flexibility of the system, it is desirable that radiocarriers could have scalable bandwidth. Thereby, the carrier could fitinto the available spectrum resource while minimizing any unused amountof frequency resources.

Therefore, the invention increases the bandwidth scalability within acurrent set of supported transmission bandwidth configurations.

The method of the invention increases the bandwidth scalability of acarrier, where the bandwidth of said carrier belongs to a set ofconfigured bandwidth configurations. The method allows for deploying acarrier with a bandwidth that is larger than the bandwidth available andusing data scheduling to control the spectral containment of the signal.The invention discloses a method using a downlink carrier on whichcell-specific reference signals can be configured with a bandwidth beingsmaller than the carrier bandwidth.

In one embodiment, the bandwidth of the reference signal is locatedsymmetrically around the center frequency of the carrier.

In one embodiment, the bandwidth of the reference signal is locatedasymmetrically around the center frequency of the carrier.

In one embodiment, the reference signal is transmitted on a set ofnon-contiguous time-frequency resources.

Two embodiments are disclosed for arranging signaling pertaining to thetime-frequency resources of the reference signal:

-   -   Signaling of time-frequency reference resources for channel        quality reporting    -   Signaling of time-frequency resources for reference signal        transmission

Furthermore, the invention discloses embodiments for signaling oftime-frequency resources of reference signal according to either;

-   -   The time-frequency positions on which the reference signal is        transmitted, or    -   the time-frequency positions on which the reference signal is        not transmitted.

The invention also comprises a radio base station and a mobile terminalhaving advantages corresponding to those of the method of the invention.

Further advantageous embodiments are disclosed in the remainingdependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments exemplifying the invention will now be described, by meansof the appended drawings, on which FIG. 1 illustrates an example where acarrier with frequency range F_(c) is smaller than the availablefrequency range F, FIG. 2 illustrates an example where a carrier withfrequency range F_(c) is larger than the available frequency range F,

FIG. 3 illustrates an example where data (grey) is scheduled withinfrequency range F and where the frequency range of the reference signal(dotted) is smaller than F_(c),

FIG. 4 illustrates an example of two non-overlapping carriers (top) andtwo overlapping carriers (bottom),

FIG. 5 illustrates an example of a carrier where the cell-specificreference signal has a frequency range (F_(RS)) smaller than the carrierfrequency range (F_(RB)), and

FIG. 6 illustrates symmetrically located reference signal (top),asymmetrically located reference signal (middle) and non-contiguousreference signal (bottom) wherein the bandwidth of the reference signalis smaller than the carrier bandwidth.

DETAILED DESCRIPTION OF THE INVENTION

In the following the invention is discussed, often in the context of aLong Term Evolution (LTE) mobile communications system. It should benoted that any such reference to LTE should be considered as an exampleintended to elucidate the invention. The invention itself is applicableto any mobile radio communications system with the right prerequisites,as discussed below.

The prior art solutions of extension carrier and carrier segments openup for more flexible usage of the available spectrum. However, a majorlimitation would occur if these new carrier types also would be confinedto a small set of bandwidths. In that case, the bandwidth granularity isnot straightforwardly increased. According to the previous example, if19 MHz is available, a 15 MHz extension carrier may need to be deployed,possibly combined with aggregation of a 3 MHz carrier. Hence, theefficient use of available bandwidth is still a problem of the prior artsolutions.

Suppose a frequency range is defined as a set of frequencies in thefrequency spectrum and that the bandwidth of such a frequency rangedenotes the difference between the largest and smallest frequencycomprising said frequency range. FIG. 1 shows an example where afrequency range F is available and a carrier (e.g., an extensioncarrier) with a frequency range F_(c) is deployed, such that thebandwidth of F_(c) is smaller than or equal to the bandwidth of F. Thebandwidth of F_(c) may be the largest supported bandwidth being smallerthan or equal to the bandwidth of F. Typically, this would leave atleast B-B_(c) Hz of spectrum unutilized, where B is the bandwidth offrequency range F and B_(c) is the bandwidth of the frequency rangeF_(c). FIG. 1 illustrates the principle of prior art, where the carrierfrequency range must be chosen to have a bandwidth being smaller thanthe bandwidth of the available frequency range.

In this invention, it is realized that the frequency range granularitycan be improved by deploying a carrier in a frequency range that has abandwidth which is larger than the bandwidth of an available frequencyrange and arrange the transmissions on the carrier such that theactually used frequency resources are within the available frequencyrange.

FIG. 2 shows an example where a frequency range F is available and acarrier with a frequency range F_(c)is deployed, such that the bandwidthof F_(c) is larger than the bandwidth of F.

In order to realize the implications of this idea for a real lifecommunications system, a note on control channels and reference signalsmay be helpful. Any such channel or signal of the carrier should beconfined to the available spectrum resource rather than to whole of the(larger) carrier itself. Control channels are discussed in thefollowing, as an example for a Long Term Evolution (LTE) system, andthen reference signals are discussed.

In LTE, the time-frequency region onto which data (i.e., PhysicalDownlink Shared Channel, PDSCH) is mapped is referred to as resourceblocks, where a resource block is defined as a first number ofconsecutive OFDM symbols in the time domain and a second number ofsubcarriers in the frequency domain. The bandwidth of a resource blockis 180 kHz and a carrier can contain up to 110 resource blocks. Sixtransmission bandwidth configurations are supported, comprising 100, 75,50, 25, 15 and 6 resource blocks, respectively, corresponding to thechannel bandwidths 20, 15, 10, 5, 3 and 1.4 MHz. The transmissionbandwidth configuration of a carrier is broadcast to the mobileterminal, named User Equipment (UE) in LTE.

The first 1 to 3 OFDM symbols in a subframe of an LTE downlink componentcarrier contain the control channels (e.g., Physical Downlink ControlChannel (PDCCH), Physical Control Format Indicator Channel (PCFICH),Physical Hybrid ARQ Indicator Channel (PHICH)). The PDCCH containsdownlink assignments for the PDSCH and uplink grants for the PhysicalUplink Shared CHannel (PUSCH). The PCFICH determines the number of OFDMsymbols available for the control channels. The PHICH is used for HARQACK/NACK feedback for the uplink. These channels may be transmitted overthe whole carrier bandwidth, which in that case would interfere with theconcept of the invention. In LTE Rel-10, carrier aggregation issupported such that a UE can simultaneously receive data on multipledownlink component carriers. The control channels may be transmitted ona different carrier than on which the data is transmitted. This isreferred to as cross-carrier scheduling. Since cross-carrier schedulingis configured per UE, all component carriers in LTE Rel-10 still containa control region, since other UEs may be scheduled data on the carrierwithout cross-carrier scheduling.

There are some measures available in order to arrange the controlchannels to be within the available spectrum resource, discussed laterin the detailed description.

Now, considering reference signals it must be realized that theyordinarily are transmitted over a whole frequency range of a downlinkcarrier and would therefore interfere with the working principle of theinvention—to employ a carrier over a smaller available spectrum resourceand abstaining from transmissions in certain frequency regions of thecarrier—if no measures were taken to confine the reference signals tothe available spectrum resource. Some properties of reference signalsare described, as an example, for an LTE system below.

A number of different reference signals are transmitted on an LTEcarrier, including:

Common Reference Signal (CRS)

These are cell-specific and are used for obtaining channel estimates forthe control and data channels, for channel quality measurements to bereported in the uplink and for mobility procedures. The CRS istransmitted over the whole carrier bandwidth, i.e., in all resourceblocks.

Channel State Information Reference Signal (CSI-RS)

These are cell-specific and are used for obtaining channel qualitymeasurements to be reported in the uplink. The CSI-RS is transmittedover the whole carrier bandwidth, i.e., in all resource blocks.

Demodulation Reference Signal (DM-RS)

These are UE-specific and are only used for obtaining channel estimatesfor data demodulation of the PDSCH. The DM-RS is only transmitted in thesame resource blocks that contain the scheduled data, i.e., where thePDSCH is for the UE.

Either a CRS or CSI-RS has to be present on a carrier in order tosupport channel quality reporting. This implies that there will be atleast one reference signal which is allocated over the whole bandwidthof either carrier segment or extension carrier. However, the bandwidthof reference signals in LTE is the same as the bandwidth of the carrier,which means that the bandwidth of a carrier may not match the availablespectrum if the reference signals are according to the prior art LTEsystem.

With the properties of reference signals in mind, the invention couldnow in a basic embodiment be described as a method for arrangingtransmissions on a downlink carrier c, spanning a frequency range F_(c),in a mobile radio communications system. In this context, the carrierspanning a frequency range means that the carrier occupies this range offrequencies in the radio spectrum where it is transmitted. Further, abandwidth of F_(c) belongs to a set of predefined channel bandwidths inthe communications system, and wherein the carrier c comprises a set ofreference signals defined in the communications system.

The method is distinguished by:

-   -   providing a configurable frequency range F_(RS) comprising a set        of time-frequency resources for comprising the reference signals        of the carrier c, and    -   signaling information associated with the configuration of said        frequency range F_(RS) to a receiver in the communications        system.

In this way, it is possible that the carrier c can be deployed over afrequency range F that is smaller than F_(c) when the frequency rangeF_(RS) is configured within F and any other transmissions on the carrierc are arranged to be within F.

So the method opens up the possibility of deploying a downlink carrierover an available frequency range that is smaller than the frequencyrange of the carrier itself, since the frequency range of the referencesignals of the carrier is configurable to not fill the whole frequencyrange of the carrier. Thus, the reference signals could be configured tobe confined to the available frequency range. Therefore, all of theavailable spectrum frequency range could be utilized, even if itsbandwidth does not correspond to any in the set of predefined channelbandwidths in the communications system.

Thus, the method of the invention could in one embodiment furthercomprise to:

-   -   configure the frequency range F_(RS) to be within F, and    -   arranging any other transmissions on the carrier c to be        within F. Thereby, making use of the configurability of the        frequency range of the reference signals.

The bandwidth of F_(c) may be a supported channel bandwidth being notsmaller than the bandwidth of F, e.g., the smallest such supportedchannel bandwidth Thus, further according to the method of theinvention, the bandwidth of F_(c) is a supported bandwidth, from the setof predefined channel bandwidths, being not smaller than the bandwidthof F. The carrier could then be operated such that transmissions shouldnot occur outside the frequency range F. Thereby, spectrum may not beunutilized.

As described previously, specifying new transmission bandwidthconfigurations in a system may be complicated, it is desirable to allowbandwidth scalability with other means. The bandwidth scalability of acarrier is limited if there are channels or signals that occupy thewhole carrier bandwidth. In LTE, this includes the control channels andreference signals. In this invention, it is realized that bandwidthscalability can be facilitated by frequency domain scheduling of datatogether with a carrier that does not require transmission of othersignals and channels over the whole bandwidth. Since user data issubject to frequency domain scheduling, it is possible to performtransmissions on any desirable frequency resources, e.g., the centralparts of the carrier. Hence, it would be possible by proprietary means(i.e., scheduler design) to accommodate the carrier in the availablespectrum resource.

FIG. 3 shows an example where a frequency range of F is available and acarrier with a frequency range F_(c)is deployed, where the bandwidth ofF_(c) is larger than the bandwidth of F. The bandwidth of F_(c) may be asupported channel bandwidth being not smaller than the bandwidth of F.The bandwidth of the cell-specific reference signal is configured to afrequency range F_(RS) having a bandwidth that is equal to the bandwidthof the frequency range F and data is scheduled within the same frequencyrange. This will minimize the amount of unused spectrum given a set ofsupported transmission bandwidth configurations. There is thus anadvantage to the system operator as the spectrum resource can be fullyutilized even if there is no bandwidth configuration that exactlymatches the frequency range F.

In prior art LTE it is required that cell-specific reference signals aretransmitted over the whole downlink carrier bandwidth. More precisely,the reference signals are transmitted in all resource blocks comprisingthe carrier. It is here disclosed a method where the frequency range ofthe cell-specific reference signals (e.g., CSI-RS) is adjustable and thebandwidth of this frequency range is less than the carrier bandwidth.This is well suited for use with an extension carrier or carriersegments, since they may not contain any other signals or channels thatcover the whole carrier bandwidth.

The method further allows for compact deployments of carriers and moreefficient use of the spectrum resources.

The traditional way of arranging contiguous radio carriers is toseparate their carrier frequencies sufficiently far apart in order tomake a guard band between the carriers. This means that two carrierswith bandwidths B₁ and B₂ should have their carrier center frequenciesseparated by at least Δƒ≧(B₁+B₂)/2. This is illustrated in the top ofFIG. 4, where the separation is Δƒ₀. One particular feature of thisinvention is that it allows overlapping of carriers. Overlapping hereimplies that a spectrum resource could contain transmissions from eitherof two carriers. This is illustrated in the bottom of FIG. 4, where theleft carrier has adjusted its transmission bandwidth of the referencesignal to be less than the carrier bandwidth. This allows that the twocarriers could be deployed with a smaller separation, Δf₁<Δf₀ andΔƒ₁<(B₁+B₂)/2. Thus, in terms of the method according to the invention,it is possible to further configure the frequency range F_(c) of carrierc overlapping with a frequency range of at least one other carrier. Theadjustment of the reference signal bandwidth and proper data schedulingwould assure that no transmissions of signals or channels from the leftcarrier coincide with transmissions on the right carrier. In principle,the data scheduling could be done independently per carrier, given thatthe set of overlapping resources is known to the schedulers of bothcarriers and are prohibited to be used for one of the schedulers. Inmore advanced cases, joint scheduling could be performed on bothcarriers. Thus, a larger bandwidth scalability has been achieved and aperson skilled in the art may configure the reference signal frequencyranges on carriers such that carriers can overlap and be separatedsufficiently close in order to fit into the available spectrum resource.This is typically practical for a set of contiguous carriers, sincetime-frequency synchronization can be maintained between carriers as touphold the orthogonality of the signal transmissions. For this, in anOFDM system, the separation ƒΔf may be a multiple of the subcarrierspacing. Additionally, if the carrier center frequencies are constrainedto be located on a pre-defined frequency raster, the separation may alsobe a multiple of the raster resolution.

The method enables that the effective carrier bandwidth can be adjustedby decreasing the bandwidth of the reference signals. Thereby thecarrier can be deployed in the available spectrum and frequency domainscheduling assures that transmissions only occur on resources that areavailable to the system operator. The outer parts of the carrier canthus be left unused and thereby act as guard bands. FIG. 5 shows oneexample where a carrier with a frequency range F_(RB) corresponding toN_(RB) resource blocks is deployed on a spectrum resource having afrequency range F_(BW) corresponding to N_(BW) resource blocks. As seen,FIG. 5 is an example where the resource blocks comprising the referencesignals are contiguously distributed in the frequency range F_(RS)corresponding to N_(RS) resource blocks. The reference signal comprisesN_(RS)<N_(RB) resource blocks. The skilled reader can interchangeablyuse the notion of frequency range instead of resource block, wheneverappropriate, or use any other entity characterizing the spectralcontainment of a signal. The bandwidth of a frequency range denotes thewidth of the range in Hertz. The above descriptions related to FIG. 1-3also apply if the terminology and notation of resource block is usedinstead of frequency range, wherein it is understood that theconfiguration of a frequency range comprising time-frequency resourcesfor comprising reference signals, can be achieved by configuring thenumber of resource blocks comprising reference signals.

This would give freedom to a person skilled in the art to configure thefrequency range F_(RS) such that the spectral containment of the signalof the carrier adheres to suitable emission requirements applicable tothe frequency range F_(BW). The skilled person in the art would alsoassure that the signal adheres to suitable emission requirements byproper data scheduling. The disclosed method therefore provides anadvantage in that the need for new transmission bandwidth configurationsdecreases while the spectrum scalability is provided by proper datascheduling and reference signal bandwidth configuration. In a typicalcase, data scheduling is confined to the frequency range defined by thereference signal.

It is noted that there may exist other channels (e.g., control channels)on the carrier that have a frequency range less than F_(RS). It is evenpossible that some control channels are specified on a frequency rangelarger than F_(RS). In prior art LTE, the actual transmission frequencyrange of some control channels is a function of the cell identity. Byproper assignment of the cell identities, it could be possible to reducethe transmission frequency range of a control channel to be less thanthe full carrier frequency range, e.g., to be contained within F_(RS).It is noted that such judicious selection of cell identities alone forcompressing the control channel frequency range complicates the networkplanning since the amount of usable cell identities decreases and itdoes not provide full frequency range scalability since the frequencyrange of the common reference signals cannot by adjusted by any means inprior art LTE.

The disclosed method is applicable on a single carrier as well as forcarrier aggregation. The method according to the invention thereforefurther comprises, in addition to any previous step, configuring thecarrier c as an aggregated carrier having a control channel on aseparate carrier in the communications system. For example, it can becombined with any of the prior art solutions extension carrier orcarrier segments. For the extension carrier, the associated controlchannels are located on a different carrier and therefore the bandwidthscalability is not constrained by the bandwidth of the control channel.For carrier segments, the associated control channels are located on thenormal LTE carrier which can be assumed to fit into the frequency rangeand therefore the bandwidth scalability is not constrained by thebandwidth of the control channel.

LTE also includes support for relays and for the communication betweenthe base station (eNodeB) and the relay node, a special control channelhas been defined, i.e., the R-PDCCH, which can be transmitted in certainsubframes. As opposed to the PDCCH, the R-PDCCH is transmitted on aconfigurable set of resource blocks and in OFDM symbols located afterthe normal control region. It therefore does not need to be transmittedover the whole carrier bandwidth. The standard allows for transmittingthe R-PDCCH in a non-interleaved manner such that only one R-PDCCH wouldbe contained in these resource blocks. This allows for using the DM-RSfor R-PDCCH reception. However, CRS must still be transmitted in thenormal control region of the subframe.

In a further example, it is realized that the disclosed method isapplicable on a single carrier for which control channels are notdefined over the whole carrier bandwidth. This could be enabled bycontrol channels that can be detected by means of UE-specificdemodulation reference signals, which therefore can be transmitted onpart of the carrier bandwidth. For example, a channel similar to theR-PDCCH in prior art relay LTE system, could be applied on a carrier forarranging transmissions instead directly between the eNodeB and the UE,and be combined with the disclosed method of a CSI-RS being configuredon less than the full carrier bandwidth.

The notion of reference signals for which the frequency range isadjustable in the context of this invention is understood to includereference signals that can be transmitted on frequency resources locatedoutside the actual frequency resources used for data transmission. Inprior art system LTE, this includes the CRS and the CSI-RS, but does notinclude the DM-RS. It is noted that the signaling for configuration ofsuch reference signals may be by dedicated or by broadcast signaling.The prior art LTE system also includes reference signals forbroadcasting (MBSFN) and positioning (PRS), which are transmitted overthe whole carrier bandwidth. Thus, the invention could apply also tothese reference signals.

In one embodiment, the frequency range of the reference signal issymmetrically divided around the center frequency of the carrier, asshown in FIG. 6 (top). This symmetry may simplify the signalingassociated with the frequency range of the reference signal.

In another embodiment, the frequency range of the reference signal isasymmetrically divided around the center frequency of the carrier, asshown in FIG. 6 (middle). This allows that different sized guard bandscould be provided which could be beneficial for contiguous carrieraggregation, i.e., when aggregated carriers are located next to eachother in frequency. A smaller guard band is typically needed between twocarriers that are time- and frequency synchronized. Since the carrierfrequency often is required to coincide with a certain frequency raster,carriers cannot be arbitrarily placed in frequency. An asymmetricalreference signal may be advantageous in this case, as it gives theadditional freedom to “move” the part of the carrier used for datatransmission in any desirable direction. This move may be obtained withlarger granularity than offered by the frequency raster.

In one embodiment, the reference signal may be transmitted onnon-contiguous time-frequency resources. The set of resources may becomprised of resource blocks, as shown in FIG. 6 (down). This gives theadditional merit that the orthogonality between reference signals indifferent cells can be improved. By avoiding transmitting the referencesignal on certain time-frequency resources in one cell, the inter-cellinterference is reduced on the same time-frequency resources in anothercell. Thus a larger frequency reuse factor is obtained for the referencesignal. This would, e.g., be beneficial in cooperative multipointtransmission schemes, where a UE receives data transmitted from multiplecells. For this, a UE typically needs to measure downlink channelqualities from multiple cells and where the respective reference signalsshould be kept orthogonal.

In one part of the invention, it is realized that the receiver (e.g., aUE) needs to be aware of the time frequency-positions of the referencesignals. In prior art LTE system, this is not an issue since both thereference symbols and their time-frequency positions can be deduced fromthe carrier bandwidth (e.g., the number of resource blocks comprisingthe carrier). However, in the disclosed invention, additional signalingof the reference signal's time-frequency positions would be needed. Thusit is a problem to arrange transmission of the reference signal suchthat the associated signaling overhead is kept small.

Granularity of the Reference Signal Bandwidth

In an OFDM system, the most detailed information describing thetime-frequency position of a reference signal would be to directlyindicate which subcarriers are used for the reference signal. In priorart LTE, a resource block is the smallest time-frequency entity to whicha data channel can be mapped. Therefore, it is realized in oneembodiment that the amount of signaling can be reduced by restrictingthe reference signal bandwidth to be a multiple of the smallesttime-frequency entity on which a data channel can be mapped, e.g., aresource block. Therefore, the method according to the invention mayfurther comprise restricting a bandwidth of the frequency range F_(RS)comprising the reference signals to a multiple of a smallesttime-frequency entity on which a data channel can be mapped in thecommunications system. Since the reference signal time-frequency patternwithin a resource block is known, a complete characterization of thereference signal can be obtained, once the set of resource blockscontaining the reference signal is known.

In a further embodiment, the method according to the invention allowsfor reducing the amount of signaling by further comprising restricting abandwidth of the frequency range F_(RS) comprising the reference signalsto a multiple of a smallest time-frequency entity used for signalingdownlink resource allocations in the communications system. In prior artLTE, to reduce the signaling overhead in the downlink control channelfor the resource allocation of the PDSCH, resource block groups (RBGs)comprising a set of resource blocks can be used as the smallest entityto which the PDSCH can be mapped. The resource block group sizeincreases with the carrier bandwidth. Therefore, it is possible toindicate which resource block groups contain the reference signal inorder to further reduce the signaling pertaining to the reference signalbandwidth.

Another embodiment of the method according to the invention allows forreducing the amount of signaling by restricting the reference signals'frequency range to the time-frequency entities used for channel qualityreporting. Thus in this step, the method comprises restricting abandwidth of the frequency range F_(RS) comprising the reference signalsto a multiple of a time-frequency entity used as a reference resourcefor channel quality reporting in the communications system. In prior artLTE, channel quality measurements obtained from the downlink referencesignals can be reported for different bandwidth parts of the carrier. Insome reporting modes, a subband, being defined as a set of contiguousresource blocks, is the smallest time-frequency entity for which channelquality measurements can be reported. Thus by letting the bandwidth ofthe reference signal be a multiple of a subband bandwidth, the signalingcan be reduced and the minimum reference signal bandwidth is providedfor channel quality reporting.

The two previous embodiments could be combined in case the subband sizeand the resource block group size are different, for which the referencesignal bandwidth should be a multiple of the largest or smallest of saidsizes in a pre-determined manner.

A further embodiment realizes that there may be limitations to thecarrier bandwidths. For example in prior art LTE, the uplink resourceallocation of the data channel (in terms of resource blocks) is amultiple of 2, 3 or 5 in order to reduce the implementation complexityof the terminal. Hence, a restriction may be that the reference signalbandwidth of the downlink should correspond to an allowed resourceallocation of an uplink carrier in the system. The method according tothe invention may therefore further comprise restricting a bandwidth ofthe frequency range F_(RS) comprising the reference signals to amultiple of a bandwidth of an allowed resource allocation of an uplinkcarrier in the communications system.

The UE is supposed to utilize the reference signals for one or severalpurposes, including channel estimation as well as channel quality basedmeasurements and therefore the time-frequency position of the referencesignals needs to be known. This information can be signaled to the UEvia broadcast messages or dedicated UE signaling. This can befacilitated by either MAC or RRC signaling. It is understood that forcarrier aggregation, such information may not necessarily have to betransmitted through channels located on the same carrier as thereference signal itself is transmitted on.

Two embodiments are disclosed for arranging signaling pertaining to thetime-frequency resources of the reference signal:

-   -   Signaling of time-frequency reference resources for channel        quality reporting    -   Signaling of time-frequency resources for reference signal        transmission

Signaling of Time-Frequency Reference Resources for Channel QualityReporting

In prior art LTE, the downlink bandwidth (in terms of resource blocks)is divided into a set S of subbands, where a subband is a set ofcontiguous resource blocks. The subbands in the set S always span thewhole carrier bandwidth and therefore the set is not signaled to the UE.Several types of channel quality measures (CQI, PMI, RI) are reported,including measures that apply to all the subbands of set S (e.g.,wideband CQI) and those that apply to some of the subbands (e.g.,subband CQI) of set S.

In one example, the time-frequency resources (e.g., resource blocks, orset S of subbands) for which the UE is supposed to report channelquality reports are signaled to the UE. The UE may assume that theassociated reference signals are transmitted within this signaledreporting bandwidth, which may not be equal to the carrier bandwidth. Inother words, the method according to the invention may further compriseimplicitly signaling, to a receiver in the communications system, theconfiguration of the frequency range F_(RS) by signaling oftime-frequency resources defined as reference resources for channelquality reporting, wherein the frequency range of the time-frequencyresources defined as reference resources for channel quality reportingcontains the frequency range F_(RS) with reference signals. Thus, inthis embodiment, the bandwidth or the frequency range of the referencesignals does not need to be explicitly signaled. The reference signalbandwidth may be larger than the reporting bandwidth. However, the UE isnot expected to measure any channel quality outside the reportingbandwidth, e.g., the set S. The person skilled in the art may arrangethe transmission of the frequency range of the reference signal suchthat its bandwidth is larger than or equal to the reporting bandwidth.It could also be possible to relate the bandwidth of the referencesignal by some predetermined rule to the reporting bandwidth, e.g., theycould be assumed to always be the same. That is, the reference signalshould be transmitted in the subbands comprising set S.

One example is where the location of the subbands comprising the carrieris represented by a bitmap which is signaled to the UE. In this case,the step of implicit signaling of the time-frequency resources definedas reference resources for channel quality reporting would beimplemented by signaling of a bitmap, where each bit in the bitmaprefers to a time-frequency resource defined as a reference resource forchannel quality reporting. A ‘1’ on a certain position in the bitmap mayimply that an associated subband should be part of the set S or viceversa.

Signaling of Time-Frequency Resources of Reference Signal

The information related to the frequency range or bandwidth of thereference signals can be describing either;

-   -   1. The time-frequency positions on which the reference signals        are transmitted, or    -   2. the time-frequency positions on which the reference signals        are not transmitted.

Alternative 1 has a straightforward interpretation while alternative 2allows a unique determination of the time-frequency positions on whichthe reference signals are transmitted if combined with information onthe total carrier bandwidth. In prior art LTE system, the number ofresource blocks of the carrier, N_(RB), is the same as the number ofresource blocks comprising the reference signal, N_(RS), and only thevalue N_(RB) is signaled. In this embodiment, also information issignaled such that the value N_(RS) can be deduced.

In the following, examples are contained exemplifying the above options.It is assumed that the transmission bandwidth configuration is from aset N_(RB)∈{N₀, . . . , N_(K)} and N_(RB)≦N_(RB) ^(max,DL).

Alternative 1

Thus, the method according to the invention may further comprisesignaling, to a receiver in the communications system, the configurationof the frequency range F_(RS). This can be done in accordance withalternative 1 above by signaling the set of time-frequency resources onwhich the reference signals are transmitted. This alternative can forinstance be further implemented in the following ways.

If the position of the reference signal is known to be symmetric aroundthe center frequency, only its bandwidth needs to be signaled. Thus, thesignaling of the configuration of the frequency range F_(RS) could beimplemented by signaling of the bandwidth of the frequency range F_(RS),when a position of the reference signals is known to be symmetric aroundthe center frequency of the carrier c. By position, it could here bemeant the number of resource blocks containing the reference signal. Theperson skilled in the art can assure that only proper values areassigned such that the reference signal is symmetrically positionedaround the center frequency. For example, if the transmission bandwidthconfiguration is an even number of resource blocks, the reference signalbandwidth should not be an odd number of resource blocks, and viceversa.

In a further example following alternative 1, the information comprisesthe number of resource blocks N_(RS)≦N_(RB) ^(max,DL) in which thereference signal is transmitted. This can be represented by a signalingformat comprising ƒ(log₂ N_(RB) ^(max,DL)) bits, where ƒ(x) is thesmallest integer not less than x. Using the knowledge on the symmetriclocation, it is realized that the number of bits could be furtherreduced by only signaling the one-sided bandwidth of the referencesignal. Thus, in this alternative the signaling of the configuration ofthe frequency range F_(RS) could be implemented by signaling a half ofthe bandwidth of the frequency range F_(RS), when a position of thereference signals is known to be symmetric around the center frequencyof the carrier c. This can be represented by a signaling formatcomprising ƒ(log₂(N_(RB) ^(max,DL)/2)) bits.

Alternative 1, Asymmetric Reference Signal Bandwidth Around CarrierCenter Frequency

An asymmetric configuration can be described by signaling the bandwidthof the reference signal and an offset value. Thus, in this alternativethe signaling of the configuration of the frequency range F_(RS) couldbe implemented by signaling of the bandwidth of the frequency rangeF_(RS) of the reference signals and an offset value from a predeterminedfrequency of the carrier c. This will uniquely determine the position ofthe reference signal. The offset value may describe a shift in frequencyposition of the reference signal bandwidth location with respect to somepredefined frequency resource, e.g., the carrier center frequency.

Alternative 1: Non-Contiguous Reference Signal

The time-frequency resources utilized by a non-contiguous referencesignal could be described by a bitmap where each bit in the bitmaprefers to, e.g., a resource block, a resource block group or a subband.The size of the bitmap is thus dependent on the number of such entities.A positive entry in the bitmap may indicate which entities contain thereference signal or vice versa. In this case, the method according tothe invention would further comprise signaling, to a receiver in thecommunications system, a non-contiguous configuration of the referencesignals within the frequency range F_(RS) by signaling of a bitmap,where each bit in the bitmap refers to a time-frequency resource amongthe set of time-frequency resources utilized or not utilized by thenon-contiguous reference signal.

Alternative 2

According to the second alternative above, the method according to theinvention would further comprise signaling, to a receiver in thecommunications system, the configuration of the frequency range F_(RS)by signaling the time-frequency positions on which the reference signalsare not transmitted, and signaling information on the total bandwidth ofcarrier c.

In an example following alternative 2, the information comprises the setof N_(RB)−N_(RS) resource blocks not containing the reference signal. Ifthere is a restriction on the value of N_(RS)≧N_(RS) ^(min,DL), asignaling format may be represented by ƒ(log₂(N_(RB) ^(max,DL)−N_(RS)^(min,DL))) bits. Otherwise, a signaling format could comprise ƒ(log₂N_(RB) ^(max,DL)) bits. Similarly as above, using the symmetric locationproperty, an alternative format can use ƒ(log₂(N_(RB) ^(max,DL)/2) bits.

Alternative 2: Asymmetric Reference Signal Bandwidth Around CarrierCenter Frequency

According to Alternative 2, a further example is to signal two values,N₁ and N₂, representing time-frequency resources (e.g., resource blocks)on the edges of the carrier on which the reference signal is nottransmitted. Knowing the carrier bandwidth expressed in number oftime-frequency resources N_(RB), the time-frequency position andbandwidth N_(RS) of the reference signal can be determined using therelation N_(RS)=N_(RB)−N₁−N₂. Expressed in terms of the method accordingto the invention, it further comprises signaling, to a receiver in thecommunications system, the configuration of the frequency range F_(RS)by:

-   -   signaling two values, N₁ and N₂, representing time-frequency        resources on the edges of the carrier c on which the reference        signal is not transmitted.

A person skilled in the art can generalize any of the above examples tothe case for signaling the set of subbands to be used for channelquality reporting instead of signaling the set of resource blockscontaining the reference signal.

A person skilled in the art can also utilize the above embodiments suchthat both the time-frequency resources for channel quality reporting andthe time-frequency resources of the reference signals are signaled. Forexample the set S can be signaled as well as information about theresource blocks containing the reference signal. Thus, the methodaccording would then comprise a combination of any of the steps forsignaling channel quality reporting above and any of the steps forsignaling the reference signals above, to further comprise signaling, toa receiver in the communications system, both time-frequency resourcesused as reference resources for channel quality reporting andinformation directly related to the time-frequency resources of thereference signals.

Backwards Compatibility

If the disclosed method is introduced in an existing system, an issuemay be that UEs currently operating in the system are assuming thereference signal is always transmitted over the whole bandwidth of acarrier. Even if signaling related to the bandwidth of the referencesignal is introduced, as disclosed above, such signaling cannot beprovided to existing UEs. In a further part of the invention, thereference signal is arranged such that backwards compatibility isachieved on a carrier.

The reference signal can be characterized by the time-frequencyresources on which it is transmitted and the modulation symbols whichare used. In this embodiment, backwards compatibility is provided byconfiguring a reference signal to use the same time-frequency resourcesand modulation symbols within a frequency range F of a carrier having abandwidth B′>B, as in said frequency range F of a carrier havingbandwidth B. Thus within a given frequency range, two carriers withdifferent bandwidths may use the same time-frequency resources andmodulation symbols for the reference signal. The method according to theinvention thus further comprises configuring the reference signals touse the same time-frequency resources and modulation symbols within afrequency range F_(c2) within carrier c, c having a bandwidth largerthan a bandwidth of the frequency range F_(c2), as for a carrier c2spanning the frequency range F_(c2) in the communications system.

An existing UE can thus be signaled a carrier bandwidth B and it willassume the reference signal bandwidth corresponds to B. UEs capable ofreceiving a reference signal not spanning the whole carrier bandwidthbut being larger than bandwidth B, can be signaled a carrier bandwidthB′ and additional information on the bandwidth of the reference signal.

In prior art LTE system, the bandwidths B′ and B should be chosen suchthat both correspond either to an even or an odd number of resourceblocks. Otherwise, the time-frequency position of the reference signalmay not be the same within the bandwidth B.

It should be noted that the method according to any of the previoussteps of the invention could be performed wherein the communicationssystem is LTE and the reference signals comprises any of CRS and CSI-RS.

Further, it should be noted that the different steps of the method ofthe invention described above could be combined arbitrarily with eachother as long as there is not inherent contradiction. An inherentcontradiction would for instance be signaling that the frequency rangeof the reference signals is located symmetrically around the centerfrequency of the of the carrier and at the same time signaling that thesame frequency range of the reference signals is located asymmetricallyaround that carrier. The skilled person would realise which steps couldof the method of the invention could be combined with other such steps.

Radio Base Station

The invention also comprises a radio base station in a mobile radiocommunications system having means for arranging transmissions on acarrier c according to any of the steps of the method of the inventiondescribed above. The skilled person has no problems of realising whatthe means for arranging the transmissions should be. For instance, forsending a radio signal, a radio transmitter is needed. For creatingspecific signals for transmission a computing device, such asmicroprocessor or a computer is needed. Computer code is needed toprovide the instructions to the computing device etc.

Mobile Terminal

The invention also comprises a mobile terminal having means forreceiving transmissions from a radio base station on a downlink carrierc, spanning a frequency range F_(c), in a mobile radio communicationssystem, wherein a bandwidth of F_(c) belongs to a set of predefinedchannel bandwidths in the communications system, and wherein the carrierc comprises a set of reference signals defined in the communicationssystem. It is distinguished by having means to receive signalinginformation associated with a configuration of a configurable frequencyrange F_(RS) comprising a set of time-frequency resources for comprisingthe reference signals of the carrier c.

The mobile terminal according to the invention may further have means tomeasure a signal quality on at least one time-frequency resource of theconfigurable set of time-frequency resources comprising the referencesignals, and having means to transmit such a signal quality measurementto the radio base station.

In fact, the mobile terminal according to the invention may have meansfor responding or reacting to any transmission from the radio basestation of the invention implementing any step of the method accordingto the invention. The skilled person realizes how the different means ofthe mobile terminal, such as the means for receiving transmissions,means for receiving signaling information, means to measure a signalquality, means to transmit a signal quality measurement, means forresponding or reacting to any transmission from the radio base stationabove, would be implemented. As for the radio base station, for sendinga radio signal, a radio transmitter is needed. For creating specificsignals for transmission a computing device, such as microprocessor or acomputer is needed. Computer code is needed to provide the instructionsto the computing device. A radio receiver is needed to receive radiosignals etc.

The invention is applicable to a single carrier operation as well ascarrier aggregation.

The invention is applicable to Frequency Division Duplex (FDD) as wellas Time Division Duplex (TDD).

The invention claimed is: 1-20. (canceled)
 21. A method for arrangingtransmissions on a downlink carrier c, spanning a frequency range F_(c),in a mobile radio communications system, wherein a bandwidth of F_(c)belongs to a set of predefined channel bandwidths in the communicationssystem, and wherein the carrier c comprises a reference signal definedin the communications system, the method comprising: providing aconfigurable frequency range F_(RS) comprising a set of time-frequencyresources for comprising the reference signal of the carrier c, andsignaling information associated with a configuration of the frequencyrange F_(RS) to a receiver in the communications system, such that thecarrier c is deployed over a frequency range F that is smaller thanF_(c) when: the frequency range F_(RS) is configured within F and anyother transmissions on the carrier c are arranged to be within F. 22.The method according to claim 21, wherein the frequency range F_(c) ofcarrier c is configured to overlap with a frequency range of at leastone other carrier.
 23. The method according to claim 21, wherein thecarrier c is configured as an aggregated carrier having a controlchannel on a separate carrier in the communications system.
 24. Themethod according to claim 21, wherein the bandwidth of F_(c) is asupported bandwidth, from the set of predefined channel bandwidths,being not smaller than the bandwidth of F.
 25. The method according toclaim 21, wherein a bandwidth of the frequency range F_(RS) isrestricted to a multiple of a smallest time-frequency entity on which adata channel can be mapped in the communications system.
 26. The methodaccording to claim 21, wherein a bandwidth of the frequency range F_(RS)is restricted to a multiple of a smallest time-frequency entity used forsignaling downlink resource allocations in the communications system.27. The method according to claim 21, wherein a bandwidth of thefrequency range F_(RS) is restricted to a multiple of a time-frequencyentity used as a reference resource for channel quality reporting in thecommunications system.
 28. The method according to claim 21, wherein abandwidth of the frequency range F_(RS) is restricted to a multiple of abandwidth of an allowed resource allocation of an uplink carrier in thecommunications system.
 29. The method according to claim 21, wherein theconfiguration of the frequency range F_(RS) is signalled implicitly tothe receiver by: signaling of time-frequency resources defined asreference resources for channel quality reporting, wherein the frequencyrange of the time-frequency resources defined as reference resources forchannel quality reporting contains the frequency range F_(RS).
 30. Themethod according to claim 29, wherein the time-frequency resourcesdefined as reference resources for channel quality reporting issignalled by: signaling of a bitmap, where each bit in the bitmap refersto a time-frequency resource defined as a reference resource for channelquality reporting.
 31. The method according to claim 21, wherein theconfiguration of the frequency range F_(RS) is signalled to the receiverby one of the following: signaling the set of time-frequency resourceson which the reference signal is transmitted; signaling the bandwidth ofthe frequency range F_(RS), when a position of the reference signal isknown to be symmetric around the center frequency of the carrier c;signaling a half of the bandwidth of the frequency range F_(RS), when aposition of the reference signal is known to be symmetric around thecenter frequency of the carrier c; and signaling the bandwidth of thefrequency range F_(RS) and an offset value from a predeterminedfrequency of the carrier c.
 32. The method according to claim 21,wherein the configuration of the frequency range F_(RS) is signalled tothe receiver by: signaling the time-frequency positions on which thereference signal is not transmitted, and signaling information on thetotal bandwidth of carrier c.
 33. The method according to claim 32,wherein the time-frequency positions on which the reference signals arenot transmitted are signalled by: signaling two values, N₁ and N₂,representing time-frequency resources on the edges of the carrier c onwhich the reference signal is not transmitted.
 34. The method accordingto claim 21, further comprising signaling, to the receiver in thecommunications system, a non-contiguous configuration of the referencesignal within the frequency range F_(RS) by: signaling of a bitmap,where each bit in the bitmap refers to a time-frequency resource amongthe set of time-frequency resources utilized or not utilized by thereference signal.
 35. The method according to claim 21, wherein theconfiguration of the frequency range F_(RS) is signalled to the receiverby signaling, to the receiver in the communications system, bothtime-frequency resources used as reference resources for channel qualityreporting and information directly related to the time-frequencyresources of the reference signal.
 36. The method according to claim 21,further comprising configuring the reference signal to use the sametime-frequency resources and modulation symbols within a frequency rangeF_(c2) within carrier c, c having a bandwidth larger than a bandwidth ofthe frequency range F_(c2), as for a carrier c2 spanning the frequencyrange F_(c2) in the communications system.
 37. The method according toclaim 21, wherein the reference signal comprises any of CRS and CSI-RS.38. A Radio base station in a mobile radio communications systemcomprising means for arranging transmissions on a carrier c according tothe steps of the method of claim
 21. 39. A mobile terminal having meansfor receiving transmissions from a radio base station on a downlinkcarrier c, spanning a frequency range F_(c), in a mobile radiocommunications system, wherein a bandwidth of F_(c) belongs to a set ofpredefined channel bandwidths in the communications system, and whereinthe carrier c comprises a reference signal defined in the communicationssystem, the mobile terminal comprising means to receive signalinginformation associated with a configuration of a configurable frequencyrange F_(RS) comprising a set of time-frequency resources for comprisingthe reference signal of the carrier c.
 40. The mobile terminal accordingto claim 39, further comprising means to measure a signal quality on atleast one time-frequency resource of the configurable set oftime-frequency resources comprising the reference signal, and means totransmit a signal quality measurement to the radio base station.